1. Field of the Invention
The present invention relates to a sealing cement, in particular a plastic-based cement which is useful for sealing mutually aligned glass plates of a liquid crystal display cell.
2. Description of the Prior Art
In the production of liquid crystal display cells, mutually aligned glass plates are sealed together with a space left between them for containing the liquid crystal material. A suitable spacing for such cells is usually from 7 to 10 .mu.m. Such cells are ordinarily produced by silk-screening a gasket-shaped layer of the sealing compound around the periphery of one of the cell plates. It is common practice to pre-treat the glass plates with a surface-active adhesion promoter, such as an organosilane compound, in order to improve the adhesion between the sealing cement and the glass surface.
The sealing cements employed for this purpose have previously been ultraviolet curing cements and especially high-temperature curing cements. These later cements are characterized by long pot times at room temperature, so that they remain workable for many hours, and even up to several days. To rapidly cure such a cement, temperatures of from 120.degree. to 180.degree. C. are required, depending upon the particular type of cement employed. At these high temperatures, however, most cements become very thin and, through capillary action in the narrow space between the cell plates, are apt to flow into and cover the display area of the cell. Thickening agents and thixotropic agents are of little help to prevent such flow because most such conventional agents lose their effectiveness at temperatures over 120.degree. C. Such cements must therefore be cured at lower temperatures which can require several hours, if they can be cured at all.
A need therefore continues to exist for a sealing cement which can be used to form a gasket-shaped layer of uniform desired thickness between the plates of a liquid crystal display cell, and which can be cured at higher temperatures without flowing into the display area of the cell.